Blocking arrangement in electric signaling systems



y 8, 1934. T. LAURENT 1,958,167

BLOCKING ARRANGEMENT IN ELECTRIC SIGNALING SYSTEMS Filed March 29, 1929 Jkfyl.

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Patented May 8, 1934 UNll'ED ST PATENT QFFHCE BLOCKING ARRANGEMENT IN ELECTRIC SIGNALING SYSTEMS Application March 29, 1929, Serial No. 351,027 In Sweden March 31, 1928 6 Claims.

The present invention relates to blocking arrangements in electric signaling systems including two circuits one of which is adapted to be made inoperative upon the second circuit being passed by current. Such systems are used by way of example in long distance, l-wire telephone lines in which speech currents in the one transmission direction have to block disturbing currents such as echo-currents or the like in the other direction. For this purpose it is previously known to dispose a short circuiting electromagnetic relay in the line circuit to be blocked said relay being madeoperative by the currents in the second circuit. In such telephone lines in which amplifying repeater sets are included it is also known to replace the electromagnetic relay by one of the valves in a repeater set the grid of said valve being subjected to a negative potential upon the second line being passed by current, whereby the anode circuit is blocked. In said known arrange ments the blocking device is, however, comparatively slow-acting and, as regards the latter arrangement, it also produces a disturbing noise in the moment of blocking in the first line.

The object of the present inventionis to eliminate said inconveniences and to bring about a blocking device operating practically instantly and without disturbing currents neither in the blocking circuit nor in the blocked circuit. The invention consists substantially therein that one or more discharge devices such as glow lamps or the like are connected into the former circuit in such a manner as to form a short circuit upon being made operative by currents in the second circuit.

The invention will be more closely described with reference to the accompanying drawing in which Figures 1 and 2 show two different embodiments of a circuit arrangement according to the invention. Figure 3 shows the circuit diagram of a detector device indicated D in Figures 1 and 2. I denotes the line which is passed by the blocking currents whereas II indicates the line to be blocked. Between thetwo lines the blocking device S, comprising the detector device D is 4 connected into circuit. When the line I transmits, by way of example, speech currents an alternating potential is supplied to the terminals (11 and c2 of the detector device D which potential generates a continuous potential between the output terminals 111 and m of the detector device of such an amplitude that the two series connected discharge devices G1 and G2, by way of example glow lamps, start discharging. Said glow-lamps or the like then form a direct current path over the two parallel connected lamps and short-circuit the line II between the points 011 and (12 thus making the line II inoperative. Two condensers C1 and C2 are connected in series with the glowlamps so as to block direct currents passing through the lamps during operation. In order to render the short circuit efiicient the resistance in the short-circuit must be comparatively small in relation to the characteristic impedance of the line and this is brought about by a transforma- 5 tion to a higher value of the line characteristic counted at the point of the short-circuit.

Such a transformation to a higher value is brought about according to the embodiment in Figure l by means of two transformers T1 and T2 0 which have a low impedance in the windings connected to the signal circuit but a high impedance in the windings connected to the glow-lamps. The shunt circuit including the glow-lamps G1 and G3 connected in parallel in relation to each other and in series with the condensers C1 and C2 respectively, brings thus about an efiicient shortcircuit between the points d1 and d2 of the curr nts in the line II. However, the two transformers T1 and T2 effect the currents in the line II the transmission qualities of which line should be normal.

In the embodiment according to Figure 2 the transformation to a higher value of the characteristic is realized over a branch line connected to the line II. After said transformation the shortcircuit takes place over the two glow-lamps G1 and G2 connected in parallel in relation to each other and in series with the condensers C1 and C2 and over the choke coil L the eifective resis- 7 tance of which is equal to approximately 4 of the ohmic resistance of the winding provided the transformer is suitably designed with small magnetic leakage.

When normallytransmitting currents over the line II the secondary circuit of the transformer T is interrupted and the line II is loaded only by the primary self-induction of the transformer. The influence on the transmitting currents on account of the connection of the transformer T into circuit becomes thus considerably less than in the former embodiment. On the other hand, the short-circuit is not quite so efficient because the short-circuit resistance must be translated to the line II over the transformer T. Which one of these two embodiments has to be preferred depends, accordingly, upon the circumstances.

As the drops of voltage in the two gIOW-Iamp are equal and opposite in the short-circuit no 110 (Ill disturbing currents in the line II are generated in the moment of establishing the short-circuit.

The purpose of the choke coil L in the embodiment according to Figure 2 which coil just as well may be included in the embodiment according to Figure 1 is to shorten the time required for completing the short-circuiting. The short-circuit is namely not delayed in this case by the charging time of the condensers C1 and C2.

Figure 3 shows a circuit diagram of an embodiment of the detector device D. The amplifying tubes F3 and F4 are supplied with a negative grid potential from the batteries V3 and V; respectively of such an amplitude that the anode current is practically equal to zero. The batteries E3 and E4 have a voltage falling below the ignition voltage of the glow-lamps G3 and G4 respectively said glow-lamps being thus unable to start glowing in the inoperative condition of the blocking device and functioning as interruptions. Upon alternating potentials entering between the terminals (21 and a: the transformer T3 superimposes alternating potentials upon the continuous voltage of the battery E3 which when reaching a certain predetermined amplitude start a discharge through the glow-lamp G3. The same concerns also the circuit E4, T4, G4. Then the upper coating of the condensers C3 or C4 respectively is charged positively which results in a displacement of the potential of the grids connected to said condenser coatings, in positive direction. After being charged the condensers C3 and C4 will discharge with a certain sluggishness through the leak resistances R3 and R4.

The device functions as follows. Alternating currents enter from the line I to the terminals a1 and a2. They pass first the transformer T3 which is dimensioned so as to have its optional working within the range of voice frequencies which involves that currents of a comparatively low frequency such as disturbing currents from a power transmission line or noises or the like are shortcircuited over the primary coil of the transformer. Provided the oscillations within said range attain the required amplitude the glowlamp G3 starts glowing which results in a displacement of the potential of the grids connected to the glow-lamp in positive direction. The leak resistance R3 is so dimensioned that the discharge through said resistance takes place with such a sluggishness that the grid voltage will vary with the modulating frequencies present in the incoming currents of voice frequencies but not with the voice frequencies themselves. In the anode circuit of the tube F3 a low frequency current is obtained corresponding to said modulating frequencies. Accordingly, the transformer T4 is di mensioned so as to operate within said range of low frequencies and transforms then the oscillations to the next valve circuit. If exceeding the predetermined amplitude the oscillations put the glow-lamp G4 into glowing and displace the potential of the grid of the tube F4 in positive direction. Here again, the leak resistance R4 is so dimensioned that the discharge through said resistance takes place with a sluggishness sufficient to damp the oscillations of modulating frequency the grid thus obtaining a comparatively constant voltage. This results in that a direct current voltage is obtained between the terminals 121 and 121 said voltage being maintained with a certain desired sluggishness which is determined by the sizes of the condenser C4 and the leak resistance R4. When said direct current voltage exceeds a certain predetermined amplitude the glow-lamps start glowing and the short-circuit of the line II is established.

From the preceding it appears that the block ing arrangement starts operation when the speech currents search a certain predetermined amplitude, the device otherwise remaining inoperative. Said predetermined value must, of course, be selected so high that the blocking device does not respond even to disturbing currents of maximum amplitude.

It is also evident that no other currents than speech currents are able to start operation of the blocking device. As previously explained, low frequency currents are without effect. Also a calling signal of voice frequency cannot pass the valve F3 because the voice frequency is damped by the leak resistance R3. Only such currents which oscillate with a modulated voice frequency such as speech currents are able to penetrate to the terminals 121 and 122 where a direct current voltage is established.

With the described detector device an instantaneous blocking effect is further assured. If solving the problem to select the speech currents by means of filter devices or the like a longer I blocking time is required on account of inertia at the building-up process of the oscillations. However, detector devices responding only to modulated voice frequencies may be arranged in several different manners.

All the described devices and circuit arrangements may, of course, be combined with other arbitrary devices and circuits without receding from the idea of the invention.

I claim.

1. An arrangement in electric signaling systems comprising in combination two transmission lines, a normally interrupted discharge device capable of independent discharge connected across one of said lines, and means under the control of the circuit of the other line for causing discharge in said discharge device upon transmission of oscillations over the line last mentioned so as to short-circuit the line first mentioned by means of said discharge device.

2. An arrangement in electric signaling systems comprising in combination two transmission lines, a normally inoperative neon tube device connected across one of said lines, and means under the control of the circuit of the other line for causing discharge in said neon tube device upon transmission of oscillations over the line last mentioned, so as to short-circuit the line first mentioned by means of said neon tube device.

3. An arrangement in electric signaling systems comprising in combination two transmission lines, a normally interrupted discharge device capable of independent discharge connected across one of said lines, and means comprising a rectifying device and arranged under the control of the circuit of the other line for causing continuous discharge in said discharge device upon transmission of oscillations over the line last mentioned so as to short-circuit the line first menside to one of said lines, two discharge devices connected in series to the output side of said rectifying device, means, comprising two condensers, for connecting said discharge devices in parallel across the other line, and means under control of the circuit of the first line for causing practically generates direct current as a result of the incoming oscillations.

6. In a two-way repeater, a pair of paths for repeating signals in opposite directions, means for disabling one of said paths in response to signals transmitted through the other of said paths, said means including a neon tube connected in said first signal repeating path, and means Whereby the signals in said second signal repeating path control the impedance of said tube.

'I'ORBERN LAURENT. 

